Rotary Shoe Direct Fluid Flow System

ABSTRACT

The circulation system for a rotary shoe features a fluid diversion to a peripheral zone from which the flow is directed by tubes or housing bores to the vicinity of the cutting structure to improve cooling and removal of debris. Some of the fluid is directed straight through into the mandrel of the tool being milled. If the formation below is at low pressure a packer cup is added to the grip tool attached to the shoe at one end and to the fish at the other end. A swivel is used to prevent the packer cup rotation. Fluid diverted by the packer cup comes up out of the mandrel and into an annular space between the mandrel and the inner wall of the shoe and out from under the shoe by flowing past the cutters. Fluid loss to the formation is minimized and cooling and cutting removal is enhanced.

FIELD OF THE INVENTION

The field of the invention is subterranean milling and more particularly where the mill washes over the stuck object such as a packer and has a fluid distribution system directed at the cutting structure with a seal option in the packer mandrel to control fluid loss during milling.

BACKGROUND OF THE INVENTION

Milling shoes are mills with peripheral cutters that descend over an object to be milled such as a packer as the cutting progresses. The cutting structure takes out the packer seal assembly as well as any slip assembly and extrusion barriers. The packer mandrel, or innermost structural member that supports a packer sealing element and slip assembly and which can be a part of an assembly of parts generally referred to as the packer body, is straddled by the hollow center of the shoe as the shoe descends as the cutting progresses, as shown in FIGS. 7-10. Pumped fluid to cool the cutting structures is delivered through the hollow core of the shoe as indicated by arrow 1. As the shoe descends and the mandrel rises in the hollow core the circulation fluid, to cool the cutters and take away the cuttings around the outside of the shoe, has to flow in the annular gap 2 between the mandrel and the inside wall of the shoe. This narrow passage creates a fluid resistance to the advance of the shoe as indicated by the arrowhead pointing up on arrow 1.

In the past when relatively soft metals such as carbon steel were being milled out a lack of optimal coolant fluid delivery to the cutters was not an issue. More recently when components have been fabricated or formed from much harder metals the technique of depending on the annular path between the mandrel and the inside wall of the shoe proved more troubling due to the longer mill times and the additional heat generated from trying to mill the harder materials. Accordingly there was a need to improve the circulation aspects of rotary shoes to improve reliability and cutting efficiency when dealing with modern materials that present added milling challenges from the materials used in the past.

In some applications the formation pressure is very low and circulating cutting fluid could be problematic if there is fluid loss through the mandrel to the formation below, indicated by arrow 3. Such fluid stream that was intended to come back to the area where the cutters are mounted through the annular space between the mandrel and the inner wall of the rotating shoe could be lost downhole and therefore would be unavailable for cooling the cutting structures and removal of debris.

The present invention improves circulation in rotating shoes by using tubes or drilled bores to direct the cooling fluid that also removes cuttings directly from the cutting structure. Furthermore the grip device for the mandrel further features a seal such as a packer cup to prevent fluid loss through the mandrel in situations with low pressure formations. These and other features of the present invention will become more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the appended claims.

SUMMARY OF THE INVENTION

The circulation system for a rotary shoe features a fluid diversion to a peripheral zone from which the flow is directed by tubes or housing bores to the vicinity of the cutting structure to improve cooling and removal of debris. Some of the fluid is directed straight through into the mandrel or body of the tool being milled. If the formation below is at low pressure a packer cup is added to the grip tool attached to the shoe at one end and to the fish at the other end. A swivel is used to prevent the packer cup rotation. Fluid diverted by the packer cup comes up out of the mandrel and into an annular space between the mandrel and the inner wall of the shoe and out from under the shoe by flowing past the cutters. Fluid loss to the formation is minimized and cooling and cutting removal is enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of the shoe milling a packer showing the fluid flow regime;

FIG. 2 shows the onset of milling and the grip device for retaining the mandrel at the conclusion of milling with the packer cup to prevent fluid loss to low pressure formations below;

FIG. 3 is the view of FIG. 2 with the shoe having descended to a milling position;

FIG. 4 is the view of FIG. 3 during milling with the packer mandrel inside the rotating shoe;

FIG. 5 is a section view along lines 5-5 in FIG. 1;

FIG. 6 is an alternative embodiment to FIG. 5;

FIG. 7 is a view of a prior art method of using a rotary shoe shown at the onset of milling;

FIG. 8 is the view of FIG. 7 further along in the milling process;

FIG. 9 is the view of FIG. 8 close to the conclusion of the milling of a packer using the rotary shoe;

FIG. 10 is an enlarged view of a portion of FIG. 9 illustrating the cooling and cutting removal flow issue with a significant washover near the end of milling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The rotary mill or shoe 10 has a lower end 12 where the cutters 14 are located on the periphery in a known manner. There is an internal open area 16 through which the mandrel 18 of the packer 20 can enter as the milling progresses. An annular gap 22 is formed between the mandrel 18 and the inner wall 24 of the shoe 10. Flow is delivered from the surface through a string that is not shown and into flow distributor 26 that has a central passage 28. Seal assemblies 30 and 32 straddle one or more lateral openings 34. Shoe 10 has a body or wall 36 that is shown in section in alternative embodiments in FIGS. 5 and 6. In FIG. 5 there are tubes 38 that start at annular space 40 shown in FIG. 1 and terminate at a lower end near the cutters 14. Alternatively, in FIG. 5 the body 36 has drilled axial holes 42 to conduct cooling fluid that removes the cuttings from the location of the cutters 14. As before the drilled holes start at annular space 40 and continue axially to the location of the cutters 14. In either alternative there are exterior axial channels 44 to direct the cuttings and fluid that drives the cuttings away from the cutters 14 and to a debris retention device that is not shown or to the surface for cuttings separation. In FIG. 5 the tubes 38 are shown in a larger recess 46 so that the tubes are protected during run in.

There are one or more small openings 48 at the lower end 50 of the flow distributor 26. That flow enters the mandrel 18 and turns around and comes out the top of the mandrel 18 and turns around again to go through the annular gap 22 and then past the cutters 14 only to turn around again to go up the outer channels 44. The final turn continues as the milling progresses because the packer 20 is still set and is blocking the annulus. Internally to the packer mandrel 18 is a gripping assembly 52 shown in FIGS. 2-4. This is a spear that retains the mandrel 18 so that the fish is not dropped when the milling concludes. It typically involves collets 54 shown schematically in a portion of the mandrel 18. Since the shoe 10 rotates but the fish or packer 20 does not, there is a swivel 56 that enables relative rotation of the shoe 10 with respect to the stationary packer 20. The swivel has a telescoping feature to allow the shoe 10 to descend during milling while allowing the relative rotation to continue.

One feature of the present invention is the addition of the seal or preferably a packer cup 58 that has the open side facing uphole. Its purpose is to prevent fluid loss through the mandrel 18 in situations where the formation below the packer is at very low pressure and thus flow through openings 48 can flow downhole into the low pressure formation but for the presence of the cup or other seal 58. While the opening or openings 48 are fairly small compared to the size of the openings 34 so that most of the flow is directed to the cutters 14, the cup seal 58 acts to avoid the fluid loss to the formation that would otherwise occur without it being there. Because the seal 58 is there additional flow that exits the port or ports 48 winds up passing the cutters 14 as well as keeping the mandrel 18 cool from the action of the rotating shoe 10 that surrounds mandrel 18 as the packer 20 is drilled out.

Those skilled in the art will appreciate that while an example of a packer being milled out is used the invention has more broad based application to other tools or equipment to be milled out. The improved circulation from the pinpointing the flow to the cutters keeps them cooler longer and enhances the milling rate as well as cuttings removal to prevent balling up the cuttings and perhaps getting the shoe stuck. The packer cup or other fluid loss device also enhances performance in the same manner and further cools the annular space between the mandrel and the rotating shoe that surrounds it as the milling progresses. The circulating flow can be directed in axial bores through the shoe body or tubes on the shoe body exterior or interior that end near the cutters. These axial passages can also be formed by an internal sleeve mounted over internal grooves in the inside wall of the shoe. The seal in the mandrel retainer can be in a variety of configurations such as a stack of chevron seals for example. The swivel permits relative rotation while a telescoping feature associated with the swivel allows relative axial movement as the shoe descends during milling relative to the stuck fish.

The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below. 

1. A milling shoe assembly for milling an object at a subterranean location and having a mandrel or body, comprising: a tubular housing having an inlet fluid passage and defined by a wall, said wall further comprising at least one peripherally mounted lower end cutter, said wall having an open lower end to advance over an object being milled by said cutter; said wall comprising at least one cutter passage extending from said inlet fluid passage to adjacent said cutters.
 2. The assembly of claim 1, wherein: said cutter passage is formed at least in part within said wall.
 3. The assembly of claim 1, wherein: said cutter passage comprises at least one tube.
 4. The assembly of claim 3, wherein: said tube is disposed in a recess on an inner or an outer face of said wall.
 5. The assembly of claim 1, wherein: a flow distributor in said inlet fluid passage further comprising an inlet and at least one lateral outlet adjacent an end of said cutter passage.
 6. The assembly of claim 5, wherein: said flow distributor further comprises spaced seals that straddle said end of said cutter passage.
 7. The assembly of claim 6, wherein: said at least one cutter comprises a plurality of cutters; said at least one cutter passage comprises a plurality of spaced passages in said wall, said wall defining an annular inlet straddled by said seals.
 8. The assembly of claim 7, wherein: said cutter passage is formed at least in part within said wall.
 9. The assembly of claim 7, wherein: said cutter passage comprises at least one tube.
 10. The assembly of claim 9, wherein: said tube is disposed in a recess on an inner or an outer face of said wall.
 11. The assembly of claim 7, wherein: said diverter having an axially oriented outlet for directing flow at the mandrel or body.
 12. The assembly of claim 11, wherein: said wall defines an annular passage between itself and the mandrel to direct flow through said axially directed outlet to said cutters.
 13. The assembly of claim 12, further comprising: a retaining device to engage the mandrel or body extending through said open lower end of said housing and supported from said housing with a swivel to allow the retaining device to remain stationary as said housing rotates; a seal on said retaining device to engage the mandrel to redirect flow from said axially oriented outlet to said cutters and away from flowing through the mandrel.
 14. The assembly of claim 1, wherein: said seal comprises at least one cup seal having an open end directed toward said axially oriented outlet.
 15. The assembly of claim 1, further comprising: a retaining device to engage the mandrel or body extending through said open lower end of said housing and supported from said housing with a swivel to allow the retaining device to remain stationary as said housing rotates; a seal on said retaining device to engage the mandrel to redirect flow from said axially oriented outlet to said cutter and away from flowing through the mandrel.
 16. The assembly of claim 15, wherein: said seal comprises at least one cup seal having an open end directed toward said fluid inlet passage.
 17. The assembly of claim 15, wherein: said cutter passage is formed at least in part within said wall.
 18. The assembly of claim 15, wherein: said cutter passage comprises at least one tube.
 19. The assembly of claim 18, wherein: said tube is disposed in a recess on an inner or an outer face of said wall. 